106 BIOMETRY 
straight line making an angle of 45 degrees with the 
base line—a line, that is to say, having a slope of 
I in I, or unity; whilst the entire absence of correlation 
would be represented by a line having no slope—that 
is to say, a horizontal line. The actual result in the 
example given is represented by a line having a slope 
of nearly I in 2, or 0°5.* 
In the following table there are set down the corre- 
lation coefficients for stature in the case of seven pairs 
of relations, as obtained from actual data of a similar 
character to that already given by way of illustration. 
TABLE V. (FROM PEARSON). 
CORRELATION COEFFICIENTS FOR HUMAN STATURE. 
Father and son . eee O'F14 
Father and daughter ... ees O'510 
Mother and son wie ees O'494 
Mother and daughter... eae 0°507 
Brother and brother ... eos O'5IL 
Sister and sister _ ees 0°537 
Brother and sister «+. eee 0°553 
Of the above, the first four values, representing 
correlation between parents and children, are seriously 
* Correlated Variability.—A precisely similar method is 
employed to measure the correlation of two parts or organs of 
the same individual. For example, the lengths of the right 
and left arms of men are very closely correlated. In order to 
attach a numerical value to this correlation the lengths of 
the right arms of a number of men are treated in the same 
way as the statures of fathers in the example given, and the 
lengths of their left arms in the same way as the statures of 
sons. The proper correlation coefficient can then be found 
by plotting the result; or the labour of plotting may be 
obviated by a-process of calculation. 
